GPS World, January 2012

THE SYSTEM GLONASS Fully Operationl For the first time in more than 15 years GLONASS is fully operational with 24 satellites in their designated orbital slots set healthy and providing world coverage GLONASS 744 an M class satellite and one of three launched from Baikonur on 4 November was set healthy December 8 bringing the number of healthy operating satellites to the full complement of 24 GLONASS briefly achieved a 24 satellite constellation in early 1996 but it degraded rapidly due to Russias economic difficulties following the break up of the Soviet Union coupled with the short lifetime of the GLONASS satellites Since 2002 the GLONASS constellation has slowly but surely been rebuilt with the Russian governments commitment to provide a global positioning and navigation system comparable to that of GPS Luch SBAS Roscosmos also launched the Luch 5A geostationary relay satellite on December 11 Luch 5A is the first in a series of new data relay satellites designed to rebuild the Luch Multifunctional Space Relay System which had ceased operating by 1998 Among other functions 5A hosts a wideband satellitebased augmentation system SBAS transponder The SBAS transponder will transmit correction and integrity data for GLONASS and GPS on the GPS L1 frequency with a C A pseudorandom noise code to be assigned by the GPS Directorate The data will be provided by the System for Differential Correction and Monitoring or SDCM which uses a ground network of monitoring stations on Russian territory as well as some overseas stations As the SDCM primary service area is Russian territory the main lobe of the SBAS antenna beam will be directed to the north with an angle of 7 degrees relative to the direction to the equator Transmitted power of 60 watts will give a signal power level at Earths surface roughly equal to that of GLONASS and GPS signals about 158 dBW The current international SBAS data format has a limited capability for broadcasting corrections for both GLONASS and GPS satellites combined There is space for only 51 satellites insufficient for the current number of satellites on orbit As a result studies are being carried out in an attempt to resolve this problem One option is to use a dynamic satellite mask where an SDCM satellite would only broadcast corrections and integrity data for those GLONASS and GPS satellites in view of users in the territory of the Russian Federation Luch 5A is the first of three MSRS SDCM satellites Luch 5B will be launched in 2012 into a slot at 95 degrees east longitude and Luch 4 in 2014 into a slot at 167 degrees east longitude Beidou Launch Fills Regional Nav System The Beidou 2 Compass IGSO 5 fifth inclined geosynchonous orbit satellite was launched on December According to a Chinese government announcement this launch completes the construction of the basic regional navigation system for service to China and will be operational by the end of the year However completion of the Phase II development to provide service to the Asia Pacific region will require further satellite launches in 2012 Phase III global coverage with a 30 satellite system will be achieved by 2020 according to the Beidou website The GNSS community outside China still awaits a Compass interface control document ICD which has been promised by the end of 2012 LightSquared Incompatibility Declared U S government tests conducted in November showed that 75 percent of GPS receivers examined were interfered with at a distance of 100 meters from a LightSquared LS base station The report states that No additional testing is required to confirm harmful interference exists and Immediate use of satellite service spectrum for terrestrial service not viable because of system engineering and integration challenges The tests showed interference by the LS Low 10 terrestrial signal with an overwhelming majority of generalpurpose GPS receivers Data from LS handsets was collected analysis is underway but no results were given Wideband and military receivers were tested but neither specifications nor results were presented a classified session was convened for that purpose Of the 92 receivers for which full data sets were compiled 75 percent of them failed a 1db test showing harmful interference at 100 meters from a LS base station These 69 receivers failed at a broadcast level of around 15dBm from the LS transmitter In a December 7 filing with the FCC LightSquared further revised its public plans to say that it would limit its power on the ground when transmitting in the lower 10 MHz from 1526 1536 MHz to no more than 30 dBm until January 1 2015 27dBm until January 1 2017 and 24dBm thereafter According to test data at 30dBm approximately 17 percent of GPS receivers would be disrupted at 27dBm 25 percent at 24dBm 36 percent Proceeding with this scenario would require the assumption that the FCC or indeed anyone believes anything that LightSquared says at any given instant for any given duration GPS World January 2012 www gpsworld 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